Quirks and Quarks

Concussions can damage the connection that helps your left brain talk to the right

A concussion disrupts the flow of information through the brain's corpus callosum which connects the left and right hemisphere.

A concussion disrupts the flow of information through the brain's corpus callosum

MRI image from a mild traumatic brain injured patient demonstrating corpus callosum fiber tractography, which is a 3D reconstruction of white matter fibers. (Melanie Wegener / RSNA)

A head injury that causes your brain to bounce around in your skull can result in a range of bad effects on your brain. A new study suggests that a concussion can even affect the flow of information between our brain's two hemispheres.

Our brains are fragile — a jelly-like mass of delicate neural fibres. A knock to the head means that fragile tissue gets banged around inside the skull we've evolved to protect it, causing bruising and tearing of neural tissue.

This can cause severe headaches and impact memory and concentration — and can create intense sensitivity to bright lights and loud sounds. 

Dr. Melanie Wegener, a resident physician at New York University Langone Health, was one of the study's co-authors. 

She wanted to study the corpus callosum, the part of the brain that separates and helps transmit signals from one hemisphere to another, because previous research had shown it was affected in concussions. 

Probing brain functionality post concussion

To test for functional damage within the corpus callosum, Dr. Wegener and her colleagues combined two innovative advances. 

The first was using a method called diffusion MRI which they used to look at the brains of concussion patients and healthy control subjects. 

"We measured and calculated various diffusion metrics, which is how well water molecules move around in structure. By looking at this, we can infer microstructural damage."

The second advance they employed was to use a visual stimulus response test to test how quickly information flows from one hemisphere to the other.

They had subjects fixate their eyes on the letter "x" in the middle of a screen, then presented short words either to the left or right of the "x" to see study their brain's processing speed. 

The right visual cortex picks up stuff in our left visual field and vice versa. But since the language centre is — for most people — in the left side of the brain, words in the left visual field take longer for people to respond to because the signal first crosses to the right visual cortex, then has to go over to the language processing side of the brain that's on the left.

"We saw that there is a relationship between the corpus callosum microstructure and the processing speed between the two hemispheres. And this relationship is altered after concussion so something is going on in the brain after concussion to effect this relationship," said Dr. Wegener.

She hopes this technique that can infer damage to the corpus callosum might one day be helpful to help track concussion treatment progression.